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Full text of "Arsenate of lead as an insecticide against the tobacco hornworms"

> . I • 







U.S. DEPARTMENT OF AGRICULTURE, 

BUREAU OF ENTOMOLOGY CIRCULAR No. 17* 

U O MOM AKI>. I ninmolosi.i iad ( h.n ol Bnu 



ARSENATE OF LEAD AS AN INSECTICIDE 
AGAINST THE TOBACCO HORNWORMS. 



BT 



A. C. MORGAN \m> D. C. PARMAX, 
Entomtlofical Assistant*. 



M047*— 18 



.TON ; OOVMNMtST mihTINO Of'ICt '•'! 










BUREAU OF ENTOMOLOGY. 

L. O. Howard, Entomologist and Chief of Bureau. 

C. L. Marlatt, Entomologist and Acting Chief in Absence of Chief. 

R. S. Clifton, Executive Assistant. 

W. F. Tastet, Chief Clerk. 

F. H. Chittenden, in charge of truck crop and stored product insect investigations. 

A. D. Hopkins, in charge of forest insect investigations. 

W. D. Hunter, in charge of southern field crop insect investigations. 

F. M. Webster, in charge of cereal and forage insect investigations. 

A. L. Quaintance, in charge of deciduous fruit insect investigations. 

E. F. Phillips, in charge of bee culture. 

D. M. Rogers, in charge of preventing spread of moths, field work. 
Rolla P. Currie, in charge of editorial work. 
Mabel Colcord, in charge of library. 

Southern Field Crop Insect Investigations. 
W. D. Hunter, in charge. 

W. D. Pierce, J. D. Mitchell, G. D. Smith, E. A. McGregor, Harry Pinkus. 

B. R. Coad, W. A. Thomas, R. W. Moreland, A. W. Jobbins-Pomeroy, C. E. 

Hester, engaged in cotton-boll weevil investigations. 
A. C. Morgan, G. A. Runner, S. E. Crumb, D. C. Parman, engaged in tobacco 

insect investigations. 

F. C. Bishopp, A. H. Jennings, H. P. Wood, W. V. King, engaged in tick investi- 
tions. 

T. E. Holloway, E. R. Barber, engaged in sugar-cane insect investigations. 

J. L. Webb,' engaged in rice insect investigations. 

R. A. Cooley, D. L. Van Dine, A. F. Conradi, C. C. Krumbhaab, collaborators. 

(ii) 



fci 



Circular No. 173. 

United States Department of Agriculture, 

BUREAU OF ENTOMOLOGY. 
L. O. HOWARD, Entomologiat and Chief of Bureau. 



ARSENATF, OF LEAD AS AN INSECTICIDE AGAINST THE 
TOBACCO BOBNWORMS. 

By A. <". MnwiAN :md I). C. I'armaN, 
Entomological AltistOntt. 

IN TKODUCTOKY. 

During the past five years the Bureau of Entomology has been 
conducting an investigation of tobacco insects in Tennessee and 
Kentucky and in some of the adjoining States. In Tennessee the 
bureau has been very materially assisted by Prof. H. A. Morgan, 
director of the Tennessee Agricultural Experiment Station. 

In the dark-tobacco districts of Kentucky and Tennessee tobacco 
hornworms are the ever-present and most serious problem of the 
tobacco grower, Ten to twelve years ago, when labor was plentiful, 
•heap, and efficient, "hand-worming" was found to be economical 
and effective in combating this pest However, during the last six or 
eight years hand-worming has become too costly, because of the 
ivity of labor, and too inefficient, and the growers have been 
forced to employ an insecticide. At the time insecticides were first 
used Paris green was found to be the safest and most efficient. Nev- 
ertheless, there has always l>oen complaint of frequent serious burn- 
ing of tobacco as a result of its use. To find a safe and effective 
insecticide has been one of the main lines of investigation by the 
writers during the past five years. Di-plunihic arsenate of lead has 
been found to meet the requirements. In the further discussion of 
this subject the use and action of Pari- green will be rather thor- 
oughly discussed in connection with the use and action of arsenate 
of lead, for the reason that since the insecticida] results of the use of 
green are so well known it will be easier to explain the value 
of arsenate of lead if it be compared with this well-known poison. 
1 



J 



2 ARSENATE OF LEAD AGAINST TOBACCO HOKNWORMS. 

NECESSITY AND ADVANTAGES OF THE USE OF AN INSECTICIDE. 

The way in which the scarcity of labor tended to bring about the 
use of an insecticide upon tobacco has already been explained. In 
addition to this necessity of using insecticides, the much greater 
efficiency of a good application of an insecticide is another strong 
argument in its favor. Hand-worming, even of the best, has many 
objections; for instance, eggs are not picked off, many small worms 
are overlooked on account of their small size, and, lastly, during the 
hot hours of the day large worms crawl down into the " ruffles " near 
the bases of the leaves and a considerable number are thus over- 
looked. On the other hand, a thorough application of an insecti- 
cide will kill practically every hornworm — except those very nearly 
full grown — within two or three days, and will also continue to kill 
the young worms that hatch several days after the application. In 
short, hand-picking has only an immediate effect in lessening the 
worms, whereas the application of an insecticide usually continues to 
kill over a period of several days. Cheapness is another point very 
greatly in favor of an insecticide as compared with hand-picking. 
The cost of keeping an acre of tobacco hand-wormed in a year when 
worms are plentiful is variously estimated at from $6 to $10. A like 
number of worms can be killed with an insecticide at a cost of not 
more than $2 or $3 an acre — sometimes less. 

THE USE OF PARIS GREEN. 

In some districts of Kentucky Paris green has been in use for over 
a decade. In the dark-tobacco districts of Kentucky and Tennessee 
it certainly was used to some extent 10 years ago and at the present 
time is in very general use. On account of the frequent injury to 
tobacco by the use of this insecticide many farmers would not use it 
if labor could be secured to do the hand-picking. On the whole, the 
cost of the Paris green plus the cost of application, plus the loss 
due to damaged tobacco, is much less than the cost of hand-worming. 
In this district the use of insecticides has come to stay. It is a neces- 
sity. 

Paris green is applied with a dust gun and without a carrier. 
From 1 to 2 pounds per acre is the usual application; 1 pound when 
worms are small (i. e., less than half grown) and 2 pounds when 
there are many worms over half grown. Success with the applica- 
tion depends upon the judgment of the farmer in choosing the time 
of application and upon the thoroughness with which the application 
is made. Much of the tobacco that is injured by Paris green is in- 
jured because of unevenness of application, or. what is too frequently 
the case, because the grower has delayed the application until half- 



IB8SNATB 01 LEAD LQAIN81 N>BACG0 HOBNWOBM 8 

grown or two-third- ^rmvn worms haw become dangerously nn- 
merous, and has then put <»n a large and uneven application with the 
bope thai he would kill all the large worms. Thia is an example of 
poor judgment. Two applications Bhouid have been made. '1 l> • 
first should have been smaller and at an earlier date in order to kill 
the worm- while small, and also to lessen the danger of burning the 
tobacco. The second application should follow as soon as. worms 
ii to increase in numbers after the first application. 

OBJECTIONS TO TH] PS] 01 PABIS QB1 i n . 

DA1TOI B K) T1IK OH KOOIi. 

There is occasionally Borne injury or irritation to the operator in 
applying Paris green. Wherever Paris green strikes the tender 
parts of the body irritation soon occurs unless a thorough bath be 
taken promptly, Bleeding at the uose sometimes occurs as ■ result of 
the irritation to the mucous membranes, For these reasons many 
people dislike to apply Paris green. However, if care is taken to 
work in a direction quartering the breeze and upon the windward 

Bide of the row while making an application, a thick sack around 
the body and a sponge over the UOSC will be found to he excellent 

preventives of irritation, particularly if followed by a hath. 

IN.ICKY BY PABIS (iBK.KN TO TOBACCO. 

The very general complaint of loss d\n' to Pan- green-burned to- 
bacOO has been found to be justified. Under favorable weather con- 
dition- 9 pounds of Pari- green per acre, sometimes more, may be 
applied without noticeable injury. On the other hand, unfavorable 
weather condition- will frequently cause injury to follow an appli- 
cation of only 1 pound per acre. Very hot -uns and low humidity 
for an extended period will produce a condition of the tobacco plant 
very susceptible to Paris-green bum. Light rains or very heavy 
.lews immediately following an application will wash the Pan- green 
down into the axil- of the leaves or into the furrows along the mid- 
ribs, and serious injury i- likely to result. 

In the Clarksville district of the dark-tobacco belt of Kentucky 
and Tennessee Paris-green burn was quite severe during l'.'ll and 
1912, particularly so in L912. Previous to these years one of the 
most careful growers in this district informed the writers that his 
I..-- on a 6-acre field of tobacco, due to Palis-green burn, amounted 
lo 8 per cent gross, which WSS a lo-- of at lea-t If. per cent of the net 
profit, and that many other growers suffered a similar lo-- in 1912. 
In 1911 the writer.- observed many fields in which the loss equaled 
or exceeded that quoted above. In L912, however, the injury by Paris 
green was more widespread than for several year-, notwithstanding 



i 



4 ARSENATE OF LEAD AGAINST TOBACCO HORN WORMS. 

the fact that many growers who suffered loss the year before were 
extremely careful in making applications. 

On January 4, 1913, the senior writer interviewed several tobacco 
buyers employed by the Italian Government. He was informed that 
several crops of tobacco the grade of which was especially suitable 
for the Italian Government were not bid upon because of the large 
percentage of tobacco injured by Paris green. The buyer stated that 
for one crop, had it been in average condition in regard to Paris- 
green injury, he would have bid 8^ cents per pound. In its damaged 
condition, however, he did not believe the crop was worth over 5 
cents per pound — a gross loss of 3^ cents per pound, or of $25 to $30 
per acre. Another crop would have received an offer of 8 cents per 
pound from the Italian buyers, but on account of Paris-green burn no 
offer was made. This buyer thought the crop worth not more than 
5| cents — a gross loss of 2^ cents per pound, or about $20 per acre. 
A third crop had its value reduced by one-half, a fourth crop was 
apparently worth about 5 cents per pound, and would ordinarily have 
brought 9 cents. This is the report of buyers of the heavier types of 
tobacco grown in this district. The lighter-bodied tobaccos undoubt- 
edly suffered as severely and probably more severely than the heavier 
tobaccos, because the lighter tobaccos are ordinarily more susceptible 
to Paris-green injury. 

Paris green injures tobacco in two ways: First, by causing dead, 
burned areas upon the leaves, where the powder has been collected by 
the dews or washed down by the rains; second, by weakening the leaf 
at the stalk. Light rains wash the insecticide into the axils of the 
leaves, and the result is that many leaves drop off before cutting time 
or become so weakened that they drop off when the plant is cut. 
Such leaves are not a total loss, for they are collected and cured, but 
they are a partial loss. They are light in weight and lack gloss and 
elasticity. 

THE USE OF ARSENATE OF LEAD. 

Arsenate of lead causes none of the injury mentioned above. Ex- 
periments performed under the direction of the senior writer showed 
that powdered arsenate of lead may be put on a fresh sucker wound 
in large quantities without causing any noticeable injury, and that 
when applied to a torn or bruised leaf it produces no injury. Paris 
green can not be applied to tobacco in the "graining" stage (i. e.. 
when nearly ripe) in sufficient quantities to do good insecticidal work 
without too grave danger of burning the plant. Arsenate of lead, on 
the other hand, can be safely applied to tobacco in the " graining " 
stage in quantities sufficient to produce satisfactory insecticidal re- 
sults. Furthermore, arsenate of lead will cause no irritation to the 



ARSENATE 0] LEAD A0AIN81 rOBACCO BOBNWOBM8. 

operator as will Puis green; in feet, thus far it bee produced do 
Doticeable injurious effects upon the operators. 

Since arsenate of lead can be applied t" tobacco without injuring 
Hie plant, and since it i> very much lees objectionable from tin- oper 
■tor's standpoint, its insecticide! properties Bhould next !>»■ disci 
A-. the dosage end action <>f Paris green arc irerj widely known, the 
value of arsenate ol lead as an in secti cide can the more easily In* 
explained by comparing it with Pans green. I In- following tables 
will serve t'> Bhos the relative values of the two insecticides under 
different conditions. 

Tabli I.- Comparison of fAe Insecticidal effects against horweortns of arsenate 
of lead and Parte grean In f'ii> w athi 





I 'ile of 
ftppU ttkn 


s 

B.d 

o » 

2 

a 

3 

V. 


Poison used. 


K summations to (hem number ol worm- killed. 


3 


o 
V. 

g 
- 

a 


On day 

-'1- 

pttad. 


On flm 

day 
alter. 


and 

day 

after, 


On 

third 


on 
fourth 

after 


on 

Oftb 

day 

;ifl>T. 


5 . 

'ft'S 
„1 

°a 

1 

E 
= 
2 




d 
> 

< 


1 

a 


d 
> 

< 


1 

Q 


d 


■o 

•: 


> 

< 


1 


d 

< 


d 
- 


d 

< 


a 


1 


".1910 

Aiu- J4 19111 
1 1911 

1,1911 


s 

1 


I-ead arsenate. 



Paris green. 

Paris green 


134 

130 
106 
135 
107 





5 
7 


40 

7.1 

h 

80 


56 
61 
49 
45 
17 


M 

35 
14 
70 
61 


29 
SI 

17 
30 
lo 






'14 






















50 


3 


5 
35 
50 


: 
23 

15 




(») 


(») 


50 


4 


31 


i 


100 


s 






100 











1 Taken on 200 plants by ordinary band-worming. 
> Uiuiy small worms alire. 

Arsenate-of-lead experiments Nos. 1 and 2 wen 1 applied under 
Very favorable conditions, i. e., there was dew upon the plants and 
do breeze. Paris-green application No. 3 was applied under equally 
favorable conditions. These three experiments killed worms very 
satisfactorily. The records in Table I were made by counting the 
worms on 60 plants of tobacco on each succeeding day after the ap- 
plication. No. 1, 5-pound dosage of arsenate of lead, gave th>- 
best results, for on the fourth day after the application only 2 live 
worms were found in hand-worming 200 hills. The 3J-pound dosage 
of arsenate of lead was not quite so good, although only 14 live worms 
were found on 200 plants the fourth day after the application. The 
Paris-green application No. 3 killed more quickly than either of the 
applications of arsenate of lead, but on the fifth day after the appli- 
cation numerous small worms were noticed in worming 200 plants. 
It was thus apparent that the Paris green was losing it> effect, owing 
to heavy dews which tended to puddle it. and to heavy drying winds 
during the day. which blew some of it from the plants. 

The application in experiment No. 4 was not made under the nm-i 
favorable conditions. There was a slight breeze during the appli- 



J 



G 



ARSENATE OF LEAD AGAINST TOBACCO HORN WORMS. 



cation; in addition, there were a large number of eggs on the plants, 
and many of the young worms hatching from these eggs were not 
killed until they wandered from the place of hatching. The same 
is true of experiment No. 5, the lf-pound dosage of Paris green. It 
will be seen, however, that experiment No. 4, the arsenate-of-lead 
application, was more effective than the Paris-green application, for 
on the day of application there were at least 140 worms in experi- 
ment No. 4, the arsenate-of-lead application, and only 114 worms in 
experiment No. 5, the Paris-green application, while on the fourth 
day after the applications there were only 31 live worms in experi- 
ment No. 4, but 52 in experiment No. 5. 

The poisons were applied in the following series of tests in the 
morning from 6.30 to 9 o'clock. The arsenate of lead was mixed with 
an equal weight of dry wood ashes. All applications were made with 
fan dust guns. The mixture of ashes and lead arsenate made a very 
good dust and compared favorably in evenness with the application 
of Paris green. Rain began to fall at 11.30 a. m. and continued in- 
termittently until 2 p. m. Part of the rain was dashing. About one- 
third of an inch fell. The first examination of the plats was made 
after 3 p. m. of the same day. The tobacco on these plats was nearly 
full grown and lapped in the rows considerably. 



Table II. — A comparison of the iiixvcticidal effects against hornworms of 
arsenate of lead and Paris green in rainy weather. 





Date of 
application. 


Dosage. 


Poison used. 


Examinations to show number of worms 
killed. 




6 

a 

a 


On day 
applied. 


On first 
day 
after. 


On 

second 

day 

after. 


On On 
third fourth 

day day 
after. 1 after. 


Size of 
worms left. 


g 

R 


> 
< 


OS 

o 

a 


d 

> 

< 


•o 

8 

a 


> 

< 


a 

© 


> 

< 


■a 9 
a .C 
a — 

O < 


3 

a 




1 


Auk. 2R.1911 
do 

do 


Pound* 
ptracrf. 

5 

4 

2J 


Lead arsenate. 
do 


59 
102 

87 


49 
21 

15 


15 

4S 

54 


41 

27 

29 


10 

21 

34 


8 
13 

14 






6 

33 

36 


2 

8 

9 


Small. 


2 






Small and 


3 


Paris green 






medium. 
Small to 








large. 



The three experiments recorded in Table II are very interesting. 
They show, first, that arsenate of lead was far more effective during 
rainy weather than was Paris green (see number of live worms on 
the fourth day), even though a very heavy dosage of Paris green 
was used; second, that to be very effective during rainy weather an 
application of at least 5 pounds of arsenate of lead per acre is re- 



ARSI \ u I "I LEAD IGAINS1 rOBACCO HORN WORMS. 7 

quired. Experiment No. ■_'. I pounds of arsenate of lead per acre, 
more affective than the -'. pounda of Piris green. AJthough a 
oonaidefable Dumber of worms were left on plat B, we Bnd thai fewer 
were alive in this experiment on the fourth day than were slive in 
the Paris green experiment, notwithstanding the fad that there weir 
practically 20 per cent more worms on No. B, the arsenate of lead 
plat, at the time of application of the poison than there were mi the 
Pari- green plat. Fortunately for the effect upon the tobacco plants, 
the rain washed off nearly all the Paris green, so that there was eery 
little burning. There was do burning of plant- on the arsenate of 
lead plats. 

Tun i- in. CotHpOfiwK of tnaectMSol effect "f pood mill poor application* i>f 

111 N- miti nj b ad. 





Dateof appti- 

lon. 


- 

c 

8 


KxniuiimiiutLs to Bad numbef of worms 
killed. 




6 

M 
- 


Day 

ap- 

pltod. 


i M 
after. 


■li v 


Thinl 


after 




M 


! 


£ 
> 

5 


— 




■d 


«J 


— 
- 


3 


\ 




1 


Aug. 16,1910 
Aug. 25,1910 


4 

31 


33 






N 


61 


41 
35 


u 


e- 


11 






I. Ill" -i pUllls 

■ 50 plants 
(•our. 


2 


• U 




















i 


On 


201 


pla 


n!-^. 











Ill T;»l>le III. which gives a comparison Of S good and I poor ap- 
plication of arsenate of lead, application \o. l. 41 pounds arsenate 
of lead per acre, was from the sump keg as application No. 2, •"•', 

pounda per acre. Counts were made on .">() hills in each instance. 
On Augu-t 10, IB10, many eggs were noticed on the plants, 90 that 
most of the worms appearing on this plat were small. It will be 
noticed that the application did not keep down the increase of WOlTOS 
due to hatching. In experiment No. 2 there were very few eggs "ii 
the plants and the worms were therefore larger than on plat 1 and 
harder to kill. Practically a clean sweep was made on No. •_'. only 
1 [ worms heing found on 200 plants on the fourth day after the 
application. Favorable weather prevailed after both applications, 
and the conditions at the time of application to both plats were 
equally favorable. What. then, is the explanation of the poor results 
on plat 1 and of the very excellent results on plat •-' *. The explana- 
tion is found in the carrier. In No. 1 the arsenate of lead WBS mixed 
thoroughly with an equal weight of finely sifted air-slaked lime, 
while in No. 2 it was thoroughly mixed with an equal weight of 
finely sifted dry wood ashes. Notwithstanding the dryness of the 



A 



8 AB6ENATE OF LEAD AGAINST TOBACCO HORNWOBMS. 

lime the mixture lumped out of the gun considerably. On the other 
hand, the arsenate of lead and ashes made a very even dust, with 
scarcely any lumping. These two experiments are here shown to 
emphasize the necessity of applying a thoroughly even dust. A 
lumpy application is a waste of time and material and will be no 
more effective than would a perfect application which had been 
rained upon immediately following the application. 

HOW TO APPLY ARSENATE OF LEAD TO TOBACCO. 

Paris green is generally applied to tobacco by means of a dust 
gun and without the admixture of a carrier. On the other hand, 
arsenate of lead must be mixed with a carrier in order to secure an 
even and thorough distribution. Several carriers have been tested 
with this insecticide. Finely sifted air-slaked lime, to our surprise, 
did not dust evenly. Road dust and land plaster proved to be too 
heavy. The best results were obtained with finely sifted, freshly burned 
wood ashes. At least an equal bulk of the wood ashes should be used. 
Mix the arsenate of lead and ashes very thorough]}' and apply while 
there is dew upon the tobacco and when there is no breeze. Even if 
very dry and finely sifted ashes are used, unsatisfactory results will 
be obtained unless the application is made with a powerful dust gun. 
The hand-power dust guns now in general use do not furnish suffi- 
cient power to make anything like a satisfactory and effective appli- 
cation. Special guns that will perform satisfactory work are gradu- 
ally coming on the market. The new guns have a fan with a diame- 
ter of 8 inches, whereas the old guns have a fan diameter of only 6 
inches. The new guns have also an auxiliary dust chamber, which 
is very essential, because the dust containers of the old guns are so 
small that they have to be refilled five or six times for each acre 
dusted. Two refillings of the new guns will be sufficient for dusting 
an acre. 

To secure the best results dust the tobacco when dew is upon the 
plants and when there is no breeze. By reference to Table III we 
see the comparative results of a good and a poor application of 
arsenate of lead. The use of a carrier that does not dust evenly, the 
application of the insecticide when there is too much breeze, and the 
use of too small a dust gun are all certain to give unsatisfactory 
results. Avoid these mistakes, and satisfactory results will be secured. 

Thoroughness of application can not be too strongly recommended. 
When tobacco worms are numerous a poor application of an insecti- 
cide will miss worms enough to ruin in two days more than enough 
tobacco to pay for the whole application. Make the application 
thorough. 



LRSENAT] .'I LEAD \..\l\si rOBACCO B0BNW0RM8. B 

ran qrao] or umnui 01 1 1 vD 10 t n loainsi red pobao 

BORN Hi, UU, 

\r 1 1 ,: if lead, theoretically, ere either triplumbic or diplumbic, 
although many of tlic grades and brands are undoubtedly a mixture 
of the (\\<>. Numerous experiments by agents of the bureau I iu \ •• 
proved thai triplumbic arsenate of lead is a very unsatisfactory 
insecticide for use against tobacco bornworms; in fact the in 
ridal action of thi> grade is bo slow that ?erj few growers would 
p( an application as ;i gift. On the other hand, an arsenate of 
lead composed almosl entirely of the diplumbic form produces very 
satisfactory insecticidaJ results when used against this insect. 

In both the triplumbic and diplumbic forms the arsenic i-. present 
as arsenic acid. Theoretically triplumbic arsenate of lead in pow- 
dered form contains 25.58 per cent of arsenic acid, while the diplum- 
bic, in powdered form, contains theoretically 88.15 per cent of 
arsenic acid. Tobacco growers should demand a powdered arsenate 
of lead that is composed largely of the diplumbic form. In order to 
be certain that the diplumbic form is predominant buy only those 

powdered arsenates of lead which the manufacturers will guarantee 
to contain at least :W per cent of arsenic acid: also insist upon a 
guaranty of not more than 1 per cent of free, or water-soluble, arseni- 
OUS acid, in order to he sure that the applications will not burn the 
tobacco. The writers advise growers and dealers who may use or 
handle powdered arsenate of lead for use against tobacco worms to 
demand a written guaranty that the composition of the products is 
as recommended above. 

WHEN TO APPLY ARSENATE OF LEAD. 

The first application of arsenate of lead should be made when 
tobacco worms become too numerous to be kept off tobacco by the 
hand-picking that is usually done while hoeing, Buckering, or topping 
tobacco. In some years B BOCOnd and even a third application may 
be necessary. The time for making these applications will be indi- 
cated by the numbers of eggs and young worm- appearing on the 
tobacco. 

\GK. OK ARSENATE OF LEAD RK.QIIRK.I). 

When tobacco is small and has not begun to lap in the row an 
application of 8J pounds of arsenate of lead per acre will be efficient. 
Full-grown tobacco should receive not Less than 5 pounds per acre. 
In water spray use 8 to 4 pounds of powdered arsenate of lead per 
100 gaUons of water. 



A 



10 ARSENATE OF LEAD AGAINST TOBACCO IKiKXWOEMS. 

COST OF ARSENATE OF I.KAI). 

The special grade of powdered arsenate of lead recommended for 
use on tobacco will cost about 22 cents per pound at the factory in 
100-pound kegs. The freight will be about 1 cent per pound, mak- 
ing the total cost 23 cents per pound to the grower. Therefore a 3£- 
pound dosage will cost about SO cents, while a 5-pound dosage will 
cost $1.15. A 2-pound dosage of Paris green costs from 50 to 55 
cents, while a dosage of 1] pounds, which is the smallest which should 
be applied, will cost about 31 to 35 cents. If the comparative cost 
of Paris green and arsenate of lead were the only question to be con- 
sidered, it would be useless to recommend arsenate of lead. The 
cost, however, for the careful grower should be a matter of strictly 
secondary consideration. The certainty of not burning the tobacco 
should more than compensate for the extra cost of this insecticide. 

SUMMARY. 

Paris green frequently burns tobacco very severely, and may 
reduce the value of the crop as much as 50 per cent in exceptional 
cases. 

It is impossible to apply an effective dosage of Paris green without 
risk of burning tobacco. 

Paris green, which is applied in dust form, is used at a dosage of 
from 1 to 2 pounds per acre. 

Arsenate of lead is safe and effective during rainy weather, while 
Paris green is dangerous and ineffective. 

It is recommended that arsenate of lead be used against the tobacco 
hornworms, and that it be applied as a dust or powder. 

The dosage of arsenate of lead in powdered form varies from 3$ 
pounds per acre to 5 pounds per acre. If applied as a spray, use 3 
to 4 pounds in 100 gallons of water. 

Arsenate of lead applied in powdered form, as here recommended, 
must be mixed with a carrier. The best carrier found so far is dry 
wood ashes, used in a bulk at least equal to the arsenate of lead. 

In applying arsenate of lead use a dust gun having a fan diameter 
of at least 8 inches. 

Apply arsenate of lead when there is no breeze and when dew is 
on the plants. 

Approved : 

James Wilson. 

Secretary of Agriculture. 

Washington, D. C, February (J. 1913. 



ADDITIONAL COPIES of this publication 
A may be procured from the Supebinteniv 
ent of Documents, Government Printing 
Office, Washington, D. C. , at 5 cents per copy 



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UNIVERSITY OF FLORIDA 



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